JP2003198117A - Soldering method and joint structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain sufficient heat resistance and fatigue strength by preventing deterioration of soldered area which occurs when electronic components are soldered to a substrate using a solder material such as an Sn-Ag system material where an Sn-Bi system material or Bi is added. <P>SOLUTION: Barrier metal layers 3b, 9b are provided to cover mother materials 3a, 9a consisting of a material including Cu at least at one of electrode 3 formed to a substrate 1 and an electrode of an electronic component 7, a material 5 including Sn and Bi is placed in contact with the barrier metal layer under the condition that the solder material is fused by supplying the solder material to these electrodes, and the electrode of the electronic component is soldered to the electrode of substrate by solidifying the solder material. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of soldering one member to another member, and more particularly, in a manufacturing process of an electronic circuit board, a land formed on the board and an electrode (for example, a lead) of an electronic component. ) And the method of soldering. Further, the present invention relates to a joint structure obtained by such a soldering method, and more particularly to an electronic circuit board.

[0002]

2. Description of the Related Art Conventionally, in a manufacturing process of an electronic circuit board used for an electronic device or the like, in order to mount an electronic component on the substrate, more specifically, a lead drawn from the electronic component and a land formed on the substrate A reflow soldering method is known as one of the methods used for electrically and physically joining the two.

In a general reflow soldering method, first, so-called cream solder (not shown) is supplied by a screen printing method onto a land which is a part of a wiring pattern formed on a substrate. Cream solder is usually composed of a mixture of solder powder made of a solder material and a flux made of rosin, an activator and a solvent. After that, the electronic component is arranged at a predetermined position on the substrate so that the lead drawn out from the electronic component adheres to the cream solder arranged on the land to be joined.
In this way, the board on which the electronic components are placed via the cream solder is heat-treated at a temperature equal to or higher than the melting point of the solder material to be used, thereby activating the flux and forming the solder material forming the solder powder in the cream solder. Once melted, other components such as flux in the cream solder are evaporated (or volatilized). Next, the molten solder material is solidified by cooling (or allowing to cool) this. The solidified solder material forms the joint between the lead of the electronic component and the land of the substrate, and electrically and physically joins them. Other components such as flux other than the solder material may be present in the joint, but such other components do not exist inside the joint because they phase-separate from the solder material during heat treatment. It can be slightly left on the surface. As a result, an electronic circuit board in which electronic components are mounted on the board by the joint portion (or soldering portion) substantially made of a solder material is obtained.

As the solder material, Sn--Pb type material,
In particular, a material having a eutectic composition (hereinafter, also simply referred to as Sn-Pb eutectic material) is generally used. Sn-P
The eutectic composition of the b-based material is the Sn-37Pb composition (that is, 3
7% by weight of Pb and the balance (63% by weight of Sn). In this eutectic composition, the Sn-Pb-based material is known to have a melting point of 183 ° C.

[0005]

In recent years, a method of disposing of electronic equipment having an electronic circuit board as described above has begun to be regarded as a problem, and lead (Pb) contained in a solder material may affect the global environment and the human body. There is concern. Therefore, there is a movement to use a lead-free solder material, that is, a lead-free solder material, in place of the Sn-Pb-based material that has been conventionally used as a solder material, and its practical application has been achieved. There is.

At present, materials having various compositions have been proposed as lead-free solder materials, one of which is Sn.
-There is a Bi-based material. As a result of recent research, the eutectic composition of the Sn-Bi-based material is approximately Sn-58Bi composition (that is, 58 wt% Bi and the balance (42 wt%) Sn).
And a Sn-B composition in this eutectic composition.
It has been found that the i-based material has a melting point of 139 ° C.

In consideration of the heat-resistant temperature of electronic parts to be mounted on a board and the heat-resistant guaranteed temperature of a product including an electronic circuit board, the melting point of the lead-free solder material is sufficiently low so as not to damage the electronic parts. It is preferable that the temperature is higher than the heat-resistant guaranteed temperature of the product. The melting point of the Sn-Bi-based material as described above is lower than the melting points of other lead-free solder materials such as Sn-Ag-based materials and further the melting points of conventional Sn-Pb-based materials, and the heat-resistant guaranteed temperature of the product is Since it is sufficiently higher than the above, there is an advantage that soldering can be performed at a low temperature, and the Sn-Bi-based material can be considered as a promising alternative candidate for the Sn-Pb-based material.

The eutectic composition of the Sn--Ag type material which is also proposed as a lead-free solder material is approximately Sn--
3.5 Ag composition (that is, a composition consisting of 3.5 wt% Ag and the balance (96.5 wt%) Sn), and in this eutectic composition, the Sn-Ag-based material has a melting point of 221 ° C. I also understand. From the viewpoint of the heat-resistant temperature of electronic components to be mounted on a board and the application of existing soldering methods, the melting point of lead-free solder materials is low enough not to damage the electronic components, and the melting point of conventional Sn-Pb-based materials is low. It is desirable that the melting point is relatively close to the melting point.
Since the melting point of the system material is higher than the melting point of the conventional Sn-Pb system material, it is difficult to apply the existing soldering method as it is using the Sn-Ag system material.

[0009] However, by adding Bi to the Sn-Ag-based material to obtain the Sn-Ag-Bi-based material, it is possible to lower the melting point and bring it closer to the melting point of the conventional Sn-Pb-based material. Has also come to understand. For example, Sn
-3Ag-3Bi-3In composition (ie 3% by weight of A
g, 3 wt% Bi, 3 wt% In and the balance (91
The composition of Sn-Ag-Bi-based material has a melting point of 210 ° C. Therefore, Sn-Ag
-Bi-based materials can also be regarded as promising alternatives for Sn-Pb-based materials.

However, in place of the Sn-Pb type material, Sn-
By using the Bi-based material or the Sn-Ag-Bi-based material, there is an advantage that the electronic component can be soldered to the substrate while avoiding the thermal damage to the electronic component. However, the electronic circuit board obtained by this has a high temperature condition. As a result of the continuous use test below, it was found that the joint between the land of the substrate and the lead of the electronic component was deteriorated, and sufficient thermal fatigue strength could not be obtained.

This is a Sn--Bi type material or Sn--Ag--
Tin (Sn) contained in the Bi-based material comes into contact with copper (Cu) used as a material for the land and the lead,
An intermetallic compound composed of Sn-Cu is formed at the joint interface between the joint and the land and between the joint and the lead, and as a result, the bismuth (Bi) concentration at the joint interface becomes relatively high. It is believed that

Hereinafter, referring to FIG. 5, in the conventional reflow soldering method described above, an electronic component is manufactured by using a cream solder containing solder powder made of Sn-Bi-based material instead of Sn-Pb-based material. The electronic circuit board 80 soldered to the board will be described.

In the electronic circuit board 80, the board 6
The land 63 formed in No. 1 and the lead 69 pulled out from the electronic component 67 are electrically and mechanically joined via the joint portion 65. The land 63 is generally made of Cu and can be formed integrally with the wiring pattern. Also,
In the lead 69, the base material 69a generally made of Cu is
It is coated with a plating 69b made of a Sn-Pb eutectic material. The joint portion 65 is formed by heat-treating cream solder, and is substantially composed of a solder material derived from solder powder, as described above.

During the heat treatment, since the solder material and the land 63 are in direct contact with each other, Cu forming the land 63 is diffused into the solder material and bonded with Sn, and Sn--Cu is formed at this contact interface. The intermetallic compound 73 is formed.

Further, during the heat treatment, the solder 69 of the solder powder is melted, and the plating 69 is generally made of a Sn--Pb eutectic material having a melting point lower than the heat treatment temperature.
b also melts, and the portion of the plating 69b that comes into contact with the molten solder material melts and diffuses into the solder material.
For this reason, the plating 69b of the lead 69 is partially peeled off, and the base material 69a comes into direct contact with the molten solder material. Therefore, in the same manner as described above, Cu forming the base material 69a of the lead 69 diffuses into the solder material and S
Bonding with n, an intermetallic compound 71 made of Sn—Cu is formed at this contact interface.

As described above, when the intermetallic compound 71 made of Sn--Cu is formed at the bonding interface, the Bi concentration is relatively increased in the local region around the intermetallic compound existing at the bonding interface. . Therefore, the phase 75 in which Bi is present in a relatively high concentration (hereinafter, simply referred to as Bi-enriched phase) is formed. In particular, when the board to which the electronic components are soldered as described above is placed under high temperature conditions for a long time, more C
u diffuses into the joint (or solder material) and becomes Sn-C
The formation of the intermetallic compound consisting of u progresses, and along with this, B
The i-enriched phase 75 is enlarged (or grown). The Bi-rich phase 75 is very brittle and is considered to cause deterioration of the joint.

In particular, when an electronic component whose leads are plated with a Sn-Pb-based material such as a Sn-Pb eutectic material as described above is used, the deterioration of the joint is remarkable. This is because the lead (Pb) contained in the lead plating material is very likely to bond with bismuth (Bi), and the Bi concentrated phase 75 is formed at the joint interface between the joint portion 65 and the lead 69 and / or the land 63. Then, Sn-Bi-P around it
It is considered that this is because the alloy composed of b is easily formed. Since such an Sn-Bi-Pb alloy has a low melting point of about 98 ° C, the Sn-Bi-Pb alloy formed in the joint melts when it is placed for a long time under high temperature conditions as described above. , Sn-Bi-P once in such a molten state
When the b alloy is formed, it is considered that the growth of such alloy phase is promoted, and as a result, the joint portion is significantly deteriorated.

At present, lead-free materials for lead plating of electronic parts are being promoted, but Sn-Pb type materials may still be used in the transitional period as in the present situation. It cannot be ignored even in such cases.

Even when a cream solder containing a solder powder made of a Sn--Pb-based material is used as in the conventional case, copper (Cu) used as a material for a land and / or a lead is bonded. Diffuse inside, Sn-P
By combining with tin (Sn) contained in the b-based material, an intermetallic compound composed of Sn—Cu can be formed at the joint interface between the joint and the land and / or the lead.
However, the intermetallic compound composed of Sn—Cu is stable, and in this case, since Bi does not exist in the joint, even if the intermetallic compound composed of Sn—Cu is formed, B
It is considered that since the i-enriched phase was not formed and the Sn-Bi-Pb alloy was not formed, the problem of deterioration of the joint portion did not occur.

In addition to Cu, a Fe-42Ni alloy material (ie, 42) is used as the base material 69a of the lead 69.
An alloy material having a composition consisting of wt% Ni and the balance (58 wt%) Fe may be used. In this case, even if the plating 69b of the lead 69 melts and diffuses into the solder material and the base material 69a and the solder material come into direct contact with each other, the intermetallic compound made of Sn—Cu is present at the interface between the lead 69 and the joint portion 65. 71 is not formed. However, Sn- is still present at the interface between the land 63 made of Cu and the joint 65.
An intermetallic compound 73 made of Cu is formed, the Bi-rich phase is enlarged, and Sn is added when the plating material contains Pb.
Since it causes the formation of a Bi-Pb alloy, there is a problem that when the obtained electronic circuit board is subjected to a continuous use test under high temperature conditions, the joint portion deteriorates and sufficient heat fatigue strength cannot be obtained. Inevitable.

The above-mentioned problems can be caused by subjecting the joint to a heat treatment for a long time. Therefore, for example, by performing reflow soldering on one side of the substrate to bond the electronic component to the substrate, and also performing reflow soldering on the other side of the substrate to bond the electronic component to the substrate, When making a so-called "double-sided reflow soldering board" as a circuit board, or by performing flow soldering on one side of the board to bond electronic components to the board and reflow soldering on the other side of the board Even when the heat treatment is performed twice or more, for example, when a so-called "single-sided flow soldering / single-sided reflow soldering substrate" is produced as an electronic circuit substrate by joining electronic components to the substrate. It is possible that the same problems as in the above test may occur.

Although the case of the Sn-Bi type material has been described in detail above, the same problem may occur with other solder materials containing at least Sn and Bi, such as Sn-Ag-Bi type material.

An object of the present invention is to use Sn- as a solder material.
Continuous use under high temperature conditions, which is a unique problem when soldering (or joining) electronic components to a board using a solder material containing Sn and Bi, such as Bi-based material and Sn-Ag-Bi-based material It is an object of the present invention to provide a soldering method capable of effectively preventing deterioration of a soldering portion (or a joint portion) due to the above, and obtaining sufficient thermal fatigue strength, and an electronic circuit board obtained by the soldering method.

[0024]

According to one aspect of the present invention, a solder material containing Sn and Bi, such as Sn-Bi-based material and Sn-Ag-Bi-based material, is used to form a first member and a first member. A method of soldering (or joining, also the same below) between two members, wherein at least one of the first member and the second member includes a base material made of a material containing Cu and a base material. A barrier metal layer for coating is provided, and by supplying (or arranging) a solder material between the first member and the second member, the solder material is brought into contact with the barrier metal layer in a molten state, and is solidified. A method is provided that includes soldering between one member and a second member.

According to the soldering method as described above, C
Since the base metal made of a material containing u is coated on the barrier metal layer and the solder material containing Sn contacts the barrier metal layer, Sn in the solder material is C contained in the base material.
Direct contact with u is avoided. As a result, Sn
-The formation of the intermetallic compound comprising Cu can be effectively suppressed or prevented so that the Bi-enriched phase is not enlarged, and preferably the Bi-enriched phase is substantially prevented from being formed. It is possible to reduce or eliminate the cause of deterioration of the soldered portion (also referred to as a joint portion in the present specification) due to continuous use under the conditions, and eventually, deterioration of thermal fatigue strength.

Therefore, according to another aspect of the present invention, a first
By supplying (or arranging) a solder material containing Sn and Bi between the first member and the second member, the solder material is brought into contact with the first member and the second member in a molten state and solidified. When soldering between the first member and the second member, a portion made of a material containing Cu provided in at least one of the first member and the second member is used as a base material, and the base material is used. There is also provided a method of providing a barrier metal layer for covering the barrier metal layer and bringing the solder material into contact with the barrier metal layer in a molten state, thereby improving the thermal fatigue strength of the soldered portion (or the joint portion).

In the present invention, when both the first member and the second member are made of a material containing Cu and Cu can diffuse from both members into the solder material (or the joint portion), In both of these members, the Cu-containing material is preferably covered with a barrier metal layer so as not to come into direct contact with the solder material.
It is possible to prevent the formation of an intermetallic compound composed of u. However, the present invention is not necessarily limited to this, and even in the case as described above, by providing only one of the barrier metal layers, the thermal fatigue strength is reduced as compared with the case without the barrier metal layer. It can be mitigated.

For example, one of the first member and the second member does not have a barrier metal layer on the surface, and at least the surface is made of a material containing lead, and the lead is melted in the solder material (or the joint). Even if it can diffuse, since the Cu base material of the other member is covered with the barrier metal layer according to the present invention, the formation of the intermetallic compound consisting of Sn—Cu is at least the barrier metal layer. Since it is prevented at the joint interface between the joint and the joint, it is possible to reduce the decrease in thermal fatigue strength as compared with the case where no barrier metal layer is provided. Of course, the member without barrier metal layer is
It is preferable that a portion of the lead-containing material that can come into contact with the solder material after melting does not contain Cu, so that an intermetallic compound composed of Sn—Cu is formed even at the joint interface between the member and the joint. Can be prevented.

In the present invention, the barrier metal layer may be composed of either a single layer or a multilayer, but Cu
It is necessary to coat the base material containing the base material so that the base material does not substantially contact the molten solder material. Therefore,
The material of the barrier metal layer does not substantially diffuse (or melt) into the molten solder material, or even if it diffuses, the base material containing Cu located below it is exposed to substantially expose the solder material. It is preferable to use a material that does not come into contact with each other. In this specification, the base material of the member to be soldered is used as a reference, and the exposed surface side in contact with the solder material is referred to as "upper" and the base material side is referred to as "lower". To do.

Further, it is preferable that the barrier metal layer is made of a conductive material so as to ensure conduction between the first member and the second member. For example, the barrier metal layer is
It can be a metal layer or a laminate thereof.

In a preferred embodiment of the present invention, the barrier metal layer may be a Ni layer (that is, a layer made of Ni, the same applies to other layers described later) or a multilayer laminate including the Ni layer. Ni hardly diffuses into the solder material even when it comes into contact with the solder material, and does not expose the base material located therebelow (thus, Cu contained in the base material does not elute into the solder material). Therefore, it is suitable for use as a material for the barrier metal layer. The Ni layer is preferably in direct contact with the base material containing Cu so as to cover the base material, but the present invention is not necessarily limited to this, and a layer made of another conductive material is provided between the Ni layer and the base material. May be provided.

When a multilayer laminate including a Ni layer is used as the barrier metal layer, the Au layer, the Pd layer and the Sn- layer are used.
At least one layer selected from the group consisting of Bi layers may be provided above the Ni layer. The Ni layer is easily oxidized in air, and its oxide has relatively poor wettability with respect to the solder material. However, the above layers, such as the Au layer, are
Since it is less likely to be oxidized than the i layer, the wettability with respect to the solder material is good. For example, barrier metal layers include Ni layer / Au layer, Ni layer / Pd layer and Ni layer / Pd layer / Au.
Layers, Ni layers / Sn-Bi layers, etc. By providing such a layer above the Ni layer to form the surface of the barrier metal layer, the wettability with respect to the solder material can be improved as compared with the case where the Ni layer is used alone as the barrier metal layer. The joint reliability (mainly joint strength) of the joint can be improved. In particular, the surface (or the uppermost layer) of the barrier metal layer is preferably the Au layer.

Layers constituting the barrier metal layer (at least one layer when the barrier metal layer is a multilayer laminate)
Can be formed by methods known in the art such as electroplating, hot dipping, displacement plating, and vapor deposition.

According to another aspect of the present invention, there is provided a joint structure in which a solder material containing Sn and Bi is used to solder between a first member and a second member. There is provided a bonded structure in which at least one of the first member and the second member includes a base material made of a material containing Cu and a barrier metal layer covering the base material.

Even with such a bonded structure, since the base metal made of a material containing Cu is coated on the barrier metal layer, as in the above-described soldering method of the present invention, Sn is used.
It is possible to effectively suppress or prevent the formation of the intermetallic compound including —Cu, and thus the enlargement of the Bi concentrated phase.
Accordingly, even when the bonded structure of the present invention is continuously used under high temperature conditions, deterioration of the bonded portion is not caused, and high heat fatigue strength can be maintained.

Such a joint structure can be obtained by the soldering method of the present invention as described above. Also in the bonded structure of the present invention, the same barrier metal layer as described above in the soldering method of the present invention can be used. When the Ni layer is used alone as the barrier metal layer, the Ni layer remains as the barrier metal layer of the bonded structure obtained by the soldering method of the present invention. When an Au layer located above is used,
When the Au layer comes into contact with the molten solder material, A
Since u elutes (or melts and diffuses) into the solder material,
It should be noted that it is not recognized as one layer constituting the barrier metal layer provided in the bonding structure. The Pd layer and the Sn-Bi layer are also the same as the Au layer.

In the soldering method, the method for improving the thermal fatigue strength of the soldered portion (or the joint portion) and the joint structure of the present invention, at least one of the first member and the second member to be soldered is It suffices that the portion containing Cu be the base material and the base material is covered with the barrier metal layer. For example, when one of the first member and the second member has a portion containing Cu and the other does not have a portion containing Cu, the one portion containing Cu (as a base material)
It is covered with a barrier metal layer. Further, for example, when both the first member and the second member have a portion containing Cu, at least one of the portions, and preferably both of them are covered with a barrier metal layer (as a base material).

In the present invention, the first member and the second member may be a substrate and an electronic component, and more specifically,
It can be an electrode provided on a substrate and an electrode of an electronic component.

Substrates such as those mentioned above include, for example, those made of paper phenolic materials, glass epoxy materials, polyimide film materials, ceramic materials, and metal materials. The electrode formed on such a substrate may be, for example, a land integrally formed with the wiring pattern, and may be formed by coating a base material made of Cu with a barrier metal layer, for example.

Further, the electronic parts as described above include semiconductor parts (for example, so-called QFP (quad flat.
Package) components, CSP (chip scale package) components, and SOP (single outside
Package parts), chip parts (eg resistors,
Capacitors, transistors, inductors, etc.) as well as connectors and the like. The electrode of such an electronic component can be, for example, a lead, a terminal, or a terminal drawn out from the electronic component, which can be formed by coating a base material made of, for example, Cu with a barrier metal layer.

However, the present invention is not limited to this, and the first
The first member and the second member can be various members to be soldered together. Therefore, according to still another aspect of the present invention, there is provided an electrical component or an electronic component soldered using a solder material containing Sn and Bi, wherein C
There is also provided an electric or electronic component having an electrode including a base material made of a material containing u and a barrier metal layer covering the base material.

In the present specification, the solder material means
Metallic materials with relatively low melting points, eg about 100-2
This is a metal material that melts at a temperature of 50 ° C.
The solder material containing Sn and Bi is a solder material containing at least Sn and Bi among such solder materials. For example, a Sn-Bi-based material or a Bi-added Sn-Ag-based material (in the present specification) Sn-Ag-Bi
Also referred to as a system material, which is a Sn-Ag-Bi material, Sn
-Ag-Bi-In material and Sn-Ag-Bi-Cu
Material). Further, the term "-based material" refers to a material having a eutectic composition of a system composed of the metal component as a center and further containing a trace amount of another metal component.
For example, the Sn-Bi-based material may mainly include a Sn-58Bi eutectic composition and may contain a trace amount of other metal components (whether intentionally added or unavoidably mixed). S
The n-Bi-based material can have a melting point of, for example, about 130-150 ° C. Further, for example, a Sn-Ag-based material added with Bi is a material mainly composed of a Sn-3.5Ag eutectic composition.
i may be added in a predetermined amount (for example, about 5% by weight or less based on the whole amount), and may further contain a trace amount of another metal component (whether intentionally added or unavoidably mixed). B
The Sn-Ag material to which i is added is, for example, about 200 to 22.
It may have a melting point of 0 ° C.

In the present invention, the soldering method is
For example, it may be carried out by both the reflow soldering method and the flow soldering method, only one side of the substrate may be soldered, or both sides of the substrate may be soldered, and the bonding structure of the present invention is Those skilled in the art will readily understand that any of these methods can be used.

The concept of preventing contact between Sn and Cu in the present invention by providing a barrier metal layer is the intermetallic compound consisting of Sn--Cu in which Sn and Cu coexist in a system containing Bi. Can be preferably used when it is desired to eliminate the adverse effects of forming a Bi-enriched phase.

Alternatively, in the soldering method of the present invention, instead of providing the barrier metal layer, the solder material supplied between the first member and the second member is melted,
The object of the present invention can also be achieved by cooling and solidifying at a cooling rate of 10 ° C./second or more, and according to another aspect of the present invention, such a soldering method and a bonding obtained thereby A structure is also provided.

In the conventional general soldering method, the cooling rate is less than 10 ° C./sec, generally about 5 ° C./sec to less than 10 ° C./sec. More specifically, the solder material) was not actively cooled. On the other hand, according to the above-mentioned method of the present invention, the cooling rate is made higher than that of the conventional method. Therefore, even if the Bi-enriched phase is formed, the Bi-enriched phase is finely dispersed by rapid solidification. That is, it is possible to effectively suppress the enlargement of the Bi-rich phase. Therefore, it is possible to eliminate the cause of deterioration of a soldered portion (also referred to as a joint portion in the present specification) due to continuous use under high temperature conditions, and eventually, deterioration of thermal fatigue strength.

Therefore, according to another aspect of the present invention, the first
By supplying (or arranging) a solder material containing Sn and Bi between the first member and the second member, the solder material is brought into contact with the first member and the second member in a molten state and solidified. When soldering between the first member and the second member, the molten solder material is cooled and solidified at a cooling rate of 10 ° C./sec or more, thereby increasing the thermal fatigue strength of the soldered portion. Methods to improve are also provided.

If the cooling rate is 10 ° C./sec or more, the thermal fatigue strength can be improved as compared with the conventional one, but the cooling rate is preferably higher, for example, about 20 ° C./sec or more, for example about 20. It is preferably -30 ° C / sec. With such a cooling rate, the thermal fatigue strength can be effectively reduced as compared with the conventional case.

In the present invention, the cooling rate means the peak temperature from the temperature profile obtained by measuring the temperature of the land (or the soldering portion) where the solder material is arranged with a thermocouple or the like, and determining the peak temperature. The average cooling rate from the time when the temperature is reached to the time when the temperature is lowered to 98 ° C. which is the melting point of the Sn—Bi—Pb alloy. The temperature of 98 ° C. is sufficiently lower than the melting point of the solder material, and it can be considered that the solder material is substantially solidified at the temperature.

It should be noted that, in the present invention, the soldering method can be understood as a method for manufacturing a joint structure in which the first member and the second member are soldered.

[0051]

BEST MODE FOR CARRYING OUT THE INVENTION (Embodiment 1) Hereinafter, one embodiment of the present invention will be described.
One embodiment will be described with reference to FIG. This embodiment relates to an embodiment of the type in which both the first member and the second member comprise a barrier metal layer. Figure 1
FIG. 3 is a schematic partial cross-sectional view of an electronic circuit board obtained by the soldering method according to this embodiment.

First, the substrate 1 and the electronic component 7 to be bonded thereto are prepared. A land 3 is formed on the substrate 1 by covering a base material 3a made of Cu with a barrier metal layer 3b made of a single Ni layer. The land 3 is formed by the following method, for example. be able to.

For example, the base material 3a made of Cu is formed integrally with the wiring pattern (not shown) on the upper surface of the substrate 1 made of glass epoxy resin by thermocompression bonding (or sticking) of copper foil and etching. The wiring pattern may have a width of, for example, about 50 to 100 μm. Then, a resist is formed in a predetermined region on the surface of the substrate 1 so as to cover the wiring pattern. At this time, the base material 3a is exposed without being covered with the resist. The height of the base material 3a (that is, the height of the wiring pattern) may be, for example, about 15 to 40 μm.

By immersing the substrate 1 on which the base material 3a is thus formed in an electrolyte solution in which Ni is dissolved and applying an appropriate voltage to the base material 3a, Ni is deposited on the surface of the base material 3a. Then, a Ni layer is formed as a barrier metal layer 3b on the surface of the base material 3a by using an electroplating method. Height of Ni layer (equal to height of barrier metal layer 3b in this embodiment)
Can be, for example, about 2-5 μm. Thus, the land 3 including the base material 3a and the barrier metal layer (Ni layer in the present embodiment) 3b covering the base material 3a can be formed on the surface of the substrate 1. The land 3 may have a rectangular contour when viewed from the top surface of the substrate 1, for example, about 0.5.
It may have a lateral width of ~ 1.5 mm and a vertical width of about 0.5-1.5 mm, but the embodiments are not so limited and may be any suitable shape and size.

In the above, the method of forming the Ni layer by the electroplating method has been exemplified, but instead of this, for example, the substrate 1 on which the base material 3a is formed is immersed in a molten Ni material for melting. A plating method, a displacement plating method in which the substrate 1 is immersed in a liquid material containing a metal for plating and the surface portion of the base material 3a is replaced with a plating metal, or N is applied to the base material 3a.
Ni covering the base material 3a by a vapor deposition method for vapor depositing i
Layers can also be formed. Such electroplating method,
The hot dipping method and the vapor deposition method can be carried out by those skilled in the art by setting appropriate conditions.

On the other hand, the electronic component 7 is provided with a lead 9. The lead 9 is formed by covering a base material 9a made of Cu with a barrier metal layer 9b made of a single Ni layer. The leads 9 are formed on the barrier metal layer 9b by the same method as described above.
Is obtained in advance by forming a Ni layer on the surface of the base material 9a, and the lead 9 can be used to manufacture the electronic component 7.

On the land 3 of the substrate 1 prepared as described above, cream solder is supplied by, for example, a screen printing method or dispensing. This cream solder is Sn-as a solder material containing Sn and Bi.
Ag-Bi-based material, for example Sn-3Ag-2.5Bi-
2.5In material or Sn-3.5Ag-0.5Bi-
Metal particles (or solder powder) made of 3In material
It is composed of dispersed flux. In the flux,
Commercial products such as rosin, activator and solvent can be used. The metal particles are, for example, about 20 to 4
It may have an average particle size of 0 μm and may be present in a proportion of about 85-90% by weight, based on the total cream solder.

Thereafter, the leads 9 of the electronic component 7 are connected to the land 3
The electronic component 7 is appropriately arranged on the substrate 1 so as to come into contact with the cream solder supplied on the substrate 1. Here, the cream solder comes into contact with the barrier metal layer 9b of the lead 9 and the barrier metal layer 3b of the land 3 to form the base material 9a.
And 3a are not contacted. Substrate 1 obtained in this manner is processed at, for example, about 215 to 240 ° C., preferably about 22.
Heat treatment is performed by passing through a heating atmosphere of 0 to 230 ° C. As a result, heat is supplied to the cream solder to melt the solder material (Sn-Ag-Bi-based material in the present embodiment) that constitutes the metal particles in the cream solder, and components such as flux other than the metal particles It is removed by evaporation (or volatilization).

At this time, the molten solder material comes into contact with the barrier metal layers 3b and 9b, but since Ni forming them is hardly melt-diffused into the molten solder material, the molten solder material is the mother material. There is no direct contact with the materials 3a and 9a. Therefore, the formation of the Sn—Cu intermetallic compound is prevented, and thus the formation of the Bi-enriched layer also does not occur.

Then, the heat-treated substrate 1 is cooled (or allowed to cool) to solidify the solder material in a molten state, thereby forming a joint portion (or soldering portion) 5 substantially made of the solder material. . By the joint portion 5, the lead 9 of the electronic component 7 and the land 3 of the substrate 1 are electrically and mechanically joined (or soldered). In this embodiment, the cooling rate of the solder material at the time of cooling the substrate may be the same as that in the conventional soldering method.

As described above, the electronic circuit board 20 in which the electronic component 7 is mounted on the board 1 is manufactured. In the obtained electronic circuit board 20, the joint interface between the lead 9 of the electronic component 7 and the joint 5 and the land 3 and the joint 5 of the substrate 1 are obtained.
At any of the bonding interfaces between and, the formation of an intermetallic compound composed of Sn-Cu is prevented, and the formation of the Bi concentrated layer is also substantially suppressed.

2 (a) and 2 (b) show an electronic circuit board of the present embodiment manufactured in the above-described manner with a thickness of about 1 μm.
Scanning electron microscope (SEM) of a cross section in the vicinity of a bonding interface between a land barrier metal layer (Ni phase) and a bonding portion (solder phase) substantially made of a solder material after heat treatment in an atmosphere of 80 ° C. It is a photograph. FIG. 2A is a photograph after heat treatment for 60 seconds, and FIG. 2B is a photograph after heat treatment for 180 seconds. As can be seen from FIGS. 2 (a) and 2 (b), 6
After both the heat treatment for 0 seconds and the heat treatment for 180 seconds, the solder phase has a homogeneous composition in the vicinity of the Ni phase.

On the other hand, as a comparative example of this embodiment, the barrier metal layer 3b of the land 3 is not provided (that is, C
the land 3 is composed only of the base material 3a made of u), and
An electronic circuit board was produced in the same manner as this embodiment except that an electronic component in which Sn-Pb plating was applied to the base material 9a was used instead of the barrier metal layer 9b of the lead 9. Figure 3
(A) and (b) show the electronic circuit board of the comparative example thus obtained after heat treatment in an atmosphere of about 180 ° C.
It is a scanning electron microscope (SEM) photograph of a cross section in the vicinity of a bonding interface between a land (Cu phase) and a bonding portion (solder phase) substantially made of a solder material. FIGS. 3 (a) and 3 (b) correspond to FIGS. 2 (a) and 2 (b), respectively. FIG. 3 (a) is a photograph after heat treatment for 60 seconds, and FIG. 3 (b) is a photograph after heat treatment for 180 seconds. is there. As shown in FIG. 3A, an intermetallic compound composed of Cu—Sn is formed between the Cu phase and the solder phase, and an Sn—Bi—Pb alloy (Cu—Sn metal in the figure) is formed around the intermetallic compound. White areas near the interstitial compound) segregate. This Sn-Bi-Pb alloy has about 1
Since it has a low melting point of 00 ° C., it is considered to be in a molten state during heat treatment. By further heat treatment, FIG. 3 (b)
As shown in Fig. 3, the Sn-Bi-Pb alloy part formed around the Cu-Sn intermetallic compound is separated from the voids (in the figure, black between the Cu-Sn intermetallic compound and the solder phase is shown). Visible part) is formed. For this reason, it is considered that the joint strength of the joint portion is reduced.

In the present embodiment, the barrier metal layer consisting of the Ni single layer is formed, but the present invention is not limited to this, and the Ni layer is formed by the same method as the Ni layer forming method. Another metal layer, for example, an Au layer may be provided above to form a barrier metal layer composed of a multilayer laminate.
Other layers such as an Au layer provided above the Ni layer may be formed, for example, with a height of about 0.01 to 0.1 μm per layer.

Further, in the present embodiment, the base material of both the land and the lead is made of Cu and both of these base materials are covered with the barrier metal layer, but the present invention is not limited to this. At least one of these contains Cu,
The base material containing Cu may be covered with the barrier metal layer. For example, when the base material of the lead is made of an Fe-42Ni alloy material and does not contain Cu, it is not always necessary to cover the base material with a barrier metal layer, and for example, plating made of a material such as Sn-Pb-based material. The base material may be covered with.

In particular, when the lead base material is plated with a Sn-Pb type material, the land base material is made of Cu,
Since it is covered with the barrier metal layer and the intermetallic compound consisting of Sn—Cu is not formed at the bonding interface between the land and the bonding portion, the Bi-concentrated phase is not enlarged and preferably substantially not formed. Even if Pb contained in the lead plating is eluted into the joint, the formation of the Sn-Bi-Pb alloy can be effectively reduced.

In the present embodiment, the Sn-Ag-Bi based material is used as the solder material containing Sn and Bi, but the present invention is not limited to this.
Similar effects can be obtained by using other materials such as n-Bi-based materials.

Further, in the present embodiment, the electronic component is soldered (or joined) to the substrate by the reflow soldering method, but the present invention is not limited to this, and is prepared in the same manner as this embodiment. The printed circuit board and the electronic component may be soldered by, for example, a flow soldering method.

(Second Embodiment) Next, another embodiment of the present invention will be described. This embodiment relates to an embodiment of a type in which both the first member and the second member do not include a barrier metal layer and the cooling rate of the solder material is made higher than in the conventional case.

In the present embodiment, a reflow furnace for general reflow soldering is used to set Sn and B
As the solder material containing i, the lead of the electronic component and the land of the substrate were soldered with a Sn-Ag-Bi-based material. For the lead of the electronic component, for example, a general electronic component such as a base material made of Cu plated with Sn—Pb may be used. Further, as the land of the substrate, a land made of Cu (one having no barrier metal layer) can be used.

The present embodiment is different from the conventional one in that after the solder material is melted during the reflow, the substrate (more specifically, the molten solder material) is actively cooled.
Specifically, first, cream solder containing a solder material in the form of solder powder on the land of the substrate is supplied by, for example, a screen printing method so that the lead of the electronic component is located on the land through the solder material. It is properly placed on the substrate, and the substrate thus obtained is placed in a reflow furnace and heat-treated. The temperature profile (quenching profile) of the land at this time is shown by the solid line in FIG. As shown in FIG. 4, the temperature of the land first rises to about 150 ° C., is maintained at this temperature for about 100 seconds, and then rises again to reach a peak temperature of about 230 ° C. At this time, the solder material (solder powder) in the cream solder supplied onto the land is melted and other components such as flux in the cream solder are evaporated (or volatilized) and removed. Then, in the present embodiment, nitrogen gas is supplied into the chamber of the reflow furnace at a flow rate of approximately 200 to 500 liters / min, while adjusting the flow rate so that a desired temperature profile is obtained. Then, the substrate is rapidly cooled to cool the solder material. Eventually, the temperature of the land drops to 98 ° C. As a result, the solder material on the land is solidified to form a joint, and the land of the substrate and the lead of the electronic component are soldered. In the reflow soldering of the present embodiment, from the time when the temperature of the land reaches the peak temperature (about 230 ° C. in the present embodiment), Sn
The average cooling rate up to the point of reaching the temperature of 98 ° C., which is the melting point of the —Bi—Pb alloy, can be, for example, about 10 ° C./sec or more, preferably about 20 to 30 ° C./sec.

As described above, an electronic circuit board having electronic components mounted on the board is manufactured. Formation of an intermetallic compound composed of Sn-Cu is prevented at both the joint interface between the lead of the electronic component and the joint portion and the joint interface between the land of the substrate and the joint portion in the obtained electronic circuit board. Moreover, the formation of the Bi-enriched layer can be substantially suppressed.

On the other hand, as a comparative example of this embodiment, the temperature profile of the land (conventional profile) during conventional reflow soldering without rapid cooling is also shown in FIG. Conventional reflow soldering generally does not actively cool. In addition, there is a case where air at a room temperature is flown into the chamber of the reflow furnace, but the flow rate is only about 50 to 100 liters / minute. In such conventional reflow soldering, the average from the time when the temperature of the land reaches the peak temperature (about 230 ° C.) to the time when the temperature of the land decreases to 98 ° C. which is the melting point of the Sn—Bi—Pb alloy. The cooling rate is from about 5 ° C./second to at most less than about 10 ° C./second. In the electronic circuit board in which the electronic component is mounted on the substrate by such a conventional reflow soldering method, the bonding interface between the lead of the electronic component and the bonding portion and the bonding interface between the land and the bonding portion of the substrate are In either case, the formation of the intermetallic compound composed of Sn—Cu cannot be prevented, and the Bi concentrated layer is enlarged. Therefore, sufficient thermal fatigue strength cannot be obtained. In particular, when soldering a lead plated with Sn-Pb to the land of the substrate, Sn-Bi-P
This may lead to the formation of b alloy, and the deterioration of the joint may occur remarkably.

In this embodiment, in order to cool and solidify the molten solder material at a cooling rate of 10 ° C./sec or more, gas cooling using nitrogen gas is used as the cooling means. The present invention is not limited to this,
Any suitable means can be used. For example, air at an appropriate temperature may be blown into the chamber of the reflow furnace with a fan or a nozzle at a sufficient flow rate, for example, toward the entire substrate or the solder material, or droplets may be sprayed onto the substrate in a mist form, or Alternatively, the solder material may be cooled by immersing the entire substrate in a liquid at an appropriate temperature, such as water.

In the present embodiment, the Sn-Ag-Bi based material is used as the solder material containing Sn and Bi, but the present invention is not limited to this.
Similar effects can be obtained by using other materials such as n-Bi-based materials.

Further, although the reflow soldering has been described in the present embodiment, the feature of the present embodiment that the soldering portion is positively cooled at a cooling rate of about 10 ° C./min or more is the flow soldering method. Can also be applied, and the same effect can be obtained in this case as well.

Although two embodiments of the present invention have been described above, the present invention is not limited to this, and it is easily understood by those skilled in the art that various modifications can be made without departing from the concept of the present invention. Will be understood.

[0078]

According to the present invention, in the method of soldering between the first member and the second member using the solder material containing Sn and Bi, the first member and the second member are A barrier metal layer is provided on at least one side of the base material using a portion made of a material containing Cu as a base material,
The solder material is brought into contact with the barrier metal layer in a molten state and solidified, whereby the first member and the second member are soldered (or joined).

According to such a soldering method, Sn in the solder material does not come into direct contact with Cu contained in the base material, whereby an intermetallic compound composed of Sn—Cu is formed, and thus Bi is enriched. It is possible to effectively suppress or prevent the enlargement of the layer, and therefore, it is possible to reduce or eliminate the cause of deterioration of the joint portion due to continuous use under high temperature conditions, and eventually, deterioration of thermal fatigue strength.

Further, according to the present invention, a joint structure in which the first member and the second member are soldered using a solder material containing Sn and Bi, At least one of the second members is provided with a joint structure including a base material made of a material containing Cu and a barrier metal layer covering the base material, and the same effect as described above can be obtained.

Alternatively, according to the present invention, instead of providing the barrier metal layer in the above-described soldering method of the present invention, a soldering method in which a molten solder material is cooled and solidified at a cooling rate of 10 ° C./sec or more. And a joint structure obtained thereby is also provided. Even by such a soldering method, the formation of the Bi-enriched layer can be effectively suppressed or prevented, so that the joint portion is deteriorated due to continuous use under high temperature conditions, and consequently the thermal fatigue strength is lowered. The cause can be reduced or eliminated.

[Brief description of drawings]

FIG. 1 is a schematic partial cross-sectional view of an electronic circuit board obtained by a soldering method according to an embodiment of the present invention.

FIG. 2 is a graph showing the vicinity of a bonding interface between a barrier metal layer (Ni phase) of a land and a bonding portion (solder phase) after heat treatment of an electronic circuit board according to one embodiment of the present invention in an atmosphere of about 180 ° C. 2 is a scanning electron micrograph of the cross section, FIG. 2 (a) shows a heat treatment for 60 seconds, and FIG.
It is a photograph after heat treatment for 80 seconds.

FIG. 3 is a scanning electron micrograph of a cross section in the vicinity of a bonding interface between a land (Cu phase) and a bonding portion (solder phase) after a heat treatment of an electronic circuit board of a comparative example in an atmosphere of about 180 ° C. , FIG. 3 (a) shows the state of FIG.
(B) is a photograph after heat treatment for 180 seconds.

FIG. 4 is a diagram showing a temperature profile of a joint portion made of the solder material of the present embodiment together with a temperature profile of a comparative example.

FIG. 5 is a schematic partial cross-sectional view of an electronic circuit board obtained by a conventional soldering method.

[Explanation of symbols]

1 substrate 3a Land base material 3b Barrier metal layer 3 land 5 Soldering part (joint part) 7 electronic components 9a Lead base material 9b Barrier metal layer 9 leads

Claims (15)

[Claims] 1. A method of soldering between a first member and a second member using a solder material containing Sn and Bi, wherein at least one of the first member and the second member comprises: A barrier metal layer is provided that includes a base material made of a material containing Cu and a barrier metal layer that covers the base material, and supplies the solder material between the first member and the second member to melt the solder material. A method comprising soldering between a first member and a second member by contacting and solidifying. 2. The first member and the second member, one of which comprises a barrier metal layer and the other of which comprises a surface made of a material containing lead, the molten solder material contacting the surface. The method according to 1. 3. The method according to claim 1, wherein the barrier metal layer comprises a Ni layer. 4. The barrier metal layer is at least one selected from the group consisting of Au layer, Pd layer and Sn—Bi layer.
The method of claim 3, further comprising one layer, the layer being above the Ni layer. 5. A method for soldering between a first member and a second member using a solder material containing Sn and Bi, which comprises soldering between the first member and the second member. A method comprising soldering between a first member and a second member by supplying a material and cooling the molten solder material at a cooling rate of 10 ° C./second or more to solidify the material. 6. The method of claim 5, wherein at least one of the first member and the second member comprises a surface made of a lead-containing material, the solder material contacting the surface in a molten state. 7. The first member is an electrode formed on a substrate, and the second member is an electrode of an electronic component.
The method described in any one of. 8. The method according to claim 1, wherein the soldering is performed by a flow soldering method or a reflow soldering method.
7. The method according to any one of to 7. 9. A joint structure in which a first member and a second member are soldered using a solder material containing Sn and Bi, and at least the first member and the second member. One is a bonded structure including a base material made of a material containing Cu and a barrier metal layer covering the base material. 10. The bonded structure of claim 9, wherein one of the first member and the second member comprises a barrier metal layer and the other comprises a surface made of a material containing lead. 11. The bonded structure according to claim 9, wherein the first member is an electrode formed on the substrate, and the second member is an electrode of an electronic component. 12. A joint structure in which a first member and a second member are soldered by using the method according to any one of claims 1 to 8. 13. An electric or electronic component which is soldered using a solder material containing Sn and Bi, wherein C
An electric or electronic component having an electrode including a base material made of a material containing u and a barrier metal layer covering the base material. 14. Sn between the first member and the second member
And a solder material containing Bi are supplied, the solder material is brought into contact with the first member and the second member in a molten state, and is solidified to solder between the first member and the second member. At this time, a barrier metal layer covering the base material is provided with a portion made of a material containing Cu provided on at least one of the first member and the second member as a base material, and a solder material is applied to the barrier metal layer. A method of improving the thermal fatigue resistance of the soldered part by bringing them into contact in a molten state. 15. Sn between the first member and the second member
And a solder material containing Bi are supplied, the solder material is brought into contact with the first member and the second member in a molten state, and is solidified to solder between the first member and the second member. Sometimes the molten solder material is 10 ℃ /
A method of improving the thermal fatigue strength of the soldered part by cooling and solidifying at a cooling rate of at least 2 seconds.